A. Field of the Invention
The present invention relates generally to providing robust power, and in particular to apparatus and methods for providing robust power using switching to selectively distribute alternating current (AC) power to several direct current (DC) power supplies.
B. Description of the Prior Art
Many power systems need robust backup power to minimize, or eliminate, power outages. A fault may occur along one of the lines, such as overloading or shorting, causing the corresponding circuit breaker to clear at the main circuit breaker box and trip open. Other failures are also possible. For example, a service technician working on something may accidentally grab the wrong power cord and unplug it, a line cord from the subsystem to the wall outlet could become damaged, or the circuit breakers (denoted by "CB") could malfunction and open. It is also possible that a line filter which conditions the power coming from an AC box could quit operating, open up, and not let all the power through. These and other faults along the line, all the way back to the main circuit breaker in the building, could cause AC power to not be available on an AC line.
One common approach to providing more robust power uses a primary AC power source and a standby AC power source. The standby AC power source is switched in when the primary AC power source goes down. In this configuration, however, all power supplies are connected, via a switch, to the primary and standby AC power sources. The switch is thrown from the primary supply to the standby supply when a problem occurs in the primary AC power source. Switching to the other supply, however, introduces a delay because all power supplies are down for at least a period of time. This system also fails to compensate for problems in a single power supply.
An alternate approach to power supply robustness is to have redundant power supplies. If a power supply goes down, a redundant supply is switched in. This system is referred to as a "2N" system because N AC power supplies are needed to operate the system, and N additional supplies provide redundancy for each supply.